Selenocyanate derived Se-incorporation into the nitrogenase Fe protein cluster.

The nitrogenase Fe protein mediates ATP-dependent electron transfer to the nitrogenase MoFe protein during nitrogen fixation, in addition to catalyzing MoFe protein-independent substrate (CO 2 ) reduction and facilitating MoFe protein metallocluster biosynthesis. The precise role(s) of the Fe protein Fe 4 S 4 cluster in some of these processes remains ill-defined. Herein, we report crystallographic data demonstrating ATP-dependent chalcogenide exchange at the Fe 4 S 4 cluster of the nitrogenase Fe protein when potassium selenocyanate is used as the selenium source, an unexpected result as the Fe protein cluster is not traditionally perceived as a site of substrate binding within nitrogenase. The observed chalcogenide exchange illustrates that this Fe 4 S 4 cluster is capable of core substitution reactions under certain conditions, adding to the Fe protein's repertoire of unique properties.